High active low-temperature vanadia-based catalyst for the oxidation of sulfur dioxide (so₂) to sulfur trioxide (so₃)

Abstract

Embodiments herein disclose a high-performance Vanadia-based catalyst designed for the efficient oxidation of sulfur dioxide (SO₂) to sulfur trioxide (SO₃) at significantly lower operating temperatures, with optimal performance around 400°C, a temperature lower than traditionally required by conventional catalysts. The catalyst consists of vanadium pentoxide (V₂O₅) as the active component, supported on naturally occurring uncalcined diatomaceous earth, combined with alkali metal promoters. A unique feature of the support material is the use of a mixture of relatively soft diatomaceous earth, exhibiting a percentage reduction of at least 35% in D50 particle size when measured by dry versus wet methods, alongside relatively hard diatomaceous earth to enhance mechanical strength. The catalyst demonstrates SO₂ conversion rates of 50-57% at 400°C and reaches a maximum of 80% at 410°C, surpassing benchmark catalysts that require higher temperatures (around 420°C) for similar conversions.

Description

[0001] High Active Low-Temperature Vanadia-Based Catalyst for the Oxidation of Sulfur Dioxide (SO2) to Sulfur Trioxide (SO3)

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS AND PRIORITY

[0003] The present application claims priority from Indian Provisional Patent Application No. 202441101521, titled “High Active Low -Temperature Vanadia-Based Catalyst for the Oxidation of Sulfur Dioxide (SO2) to Sulfur Trioxide (SO3), ” filed on 20th December 2024. The contents of the said provisional application are incorporated herein in their entirety.

[0004] FIELD OF THE INVENTION:

[0005] The present invention relates to heterogeneous catalysis and, in particular, to vanadium-based catalysts for the oxidation of sulfur dioxide (SO2) to sulfur tri oxide (SO3). The invention is applicable to industrial sulfuric acid manufacturing processes and flue gas treatment systems requiring efficient SO2 conversion at reduced operating temperatures. The invention further relates to methods for preparing such catalysts with improved mechanical stability and corrosion-free manufacturing.

[0006] BACKGROUND OF THE INVENTION

[0007] The oxidation of sulfur dioxide (SO2) to sulfur trioxide (SO3) is a critical process in the production of sulfuric acid (H2SO4), which is a fundamental chemical used across various industrial sectors, including fertilizers, chemicals, petroleum refining, and emissions control. Efficient conversion of SO2 to SO3 is crucial not only for sulfuric acid production but also for managing industrial flue gas emissions, particularly from power plants and manufacturing facilities.

[0008] In current commercial processes, SO2 oxidation catalysts, typically based on vanadium pentoxide (V2O5), operate at temperatures near or above 420°C to achieve acceptable reaction rates. However, due to the reversible nature of the SO2 oxidation reaction, high temperatures limit the overall conversion efficiency. To overcome this, multiple catalytic beds are employed in a reactor, with each bed operating at progressively lower temperatures. Intermediate gas cooling between beds further enhances the catalyst's performance by reducing the gas temperature, allowing for improved SO2 conversion. While these strategies are effective to some extent, current catalysts face several challenges. The performance of existing catalysts significantly declines at temperatures below 400°C. Even the most advanced commercial catalysts fail to achieve sufficient conversion rates at these lower temperatures, forcing manufacturers to operate at higher temperatures, which increases energy consumption and overall operational costs. This is particularly problematic in industries with stringent energy efficiency and environmental requirements.

[0009] To address the issue of unreacted SO2, manufacturers often implement gas scrubbing systems to remove residual SO2 from the tail gas. However, this approach complicates the process and adds to operational expenses. Furthermore, many existing catalysts suffer from mechanical instability, resulting in material crushing over time, which increases the pressure drop in the reactor and reduces system efficiency. This mechanical degradation often leads to frequent maintenance and downtime.

[0010] Additionally, the manufacturing of conventional catalysts typically involves the use of sulfuric acid (H2SO4), which can cause corrosion of equipment, further increasing costs and complicating the production process. The use of noble metals like rhodium (Rh), ruthenium (Ru), and gold (Au) in some catalysts has been explored to enhance catalytic activity at lower temperatures. However, the high cost of these metals makes such catalysts impractical for large-scale industrial applications.

[0011] Despite these strategies, existing catalysts face several key challenges:

[0012] Patents such as US 1,941,426 and US 3,789,019 describe catalysts promoted with alkali metals like cesium (Cs) and rubidium (Rb) to improve their low-temperature activity. However, even with these enhancements, the catalysts still require operating temperatures around 400°C or higher, which leads to increased energy consumption and operational costs. The catalysts also struggle to achieve efficient conversion below 400°C, resulting in poor performance for industries with stringent energy efficiency requirements.

[0013] Catalysts described in US 4,193,894 and US 5,175,136 suffer from mechanical instability over prolonged operation. The use of diatomaceous earth as a support material often results in catalyst crushing over time, which increases the pressure drop (AP) in the reactor and reduces the overall efficiency of the system. The mechanical degradation of the catalyst material is a persistent problem that leads to frequent maintenance and downtime.

[0014] Noble metal-promoted catalysts, such as those disclosed in US 4,931,418 and WO 2012 / 057794 Al, improve catalytic activity at lower temperatures by incorporating expensive metals like rhodium (Rh), ruthenium (Ru), and gold (Au). However, these noble metal catalysts come at a significantly higher cost, making them impractical for large-scale industrial applications, particularly in cost-sensitive industries like sulfuric acid production.

[0015] Many current catalyst manufacturing processes involve the use of sulfuric acid (H2SO4), as seen in US 2003 / 0157010A1. The use of sulfuric acid in catalyst preparation can cause severe corrosion of the tools and equipment used in production, leading to increased maintenance costs and shortened equipment lifespan. Additionally, the handling of sulfuric acid poses environmental and safety concerns, complicating the overall manufacturing process.

[0016] Existing solutions require high operating temperatures to achieve acceptable SO2 conversion rates, limiting the energy efficiency of the process. This challenge is evident in prior art such as US 5,264,200, which still requires temperatures above 400°C to achieve efficient SO2 oxidation. While noble metals improve catalyst performance, their high cost restricts their use in industrial applications. For example, US 4,931,418 describes catalysts using cesium pyrosulfates and vanadium pentoxide (V2O5), but the reliance on expensive components increases production costs.

[0017] The mechanical instability of current catalysts leads to material crushing, which increases the pressure drop across the catalytic bed. This is a significant issue in catalysts such as those described in US 8323610B2, which also highlights the need for improved stability to prevent fines generation and catalyst degradation.

[0018] As shown in patents such as US 2003 / 0157010A1, the use of sulfuric acid in the preparation process of catalysts causes corrosion of tools and equipment. This increases costs related to maintenance and equipment replacement, further complicating the industrial production of these catalysts.

[0019] The limitations of existing solutions, including the high operating temperatures required, mechanical instability, and the need for scrubbing systems to handle residual SO2, highlight the need for a new catalyst that can operate efficiently at lower temperatures while delivering higher SO2 conversion rates.

[0020] The present invention offers a novel Vanadia-based catalyst supported on diatomaceous earth and enhanced with alkali metal sulphates such as Alkali Metal Sulphate (M2SO4) & Bisulfate (HSO4) This invention addresses the limitations of prior catalysts and provides a number of advantages, including double the SO2 Conversion at 400°C. By addressing the key challenges of high operating temperatures, mechanical instability, high production costs, and corrosion issues, the present invention represents a significant advancement over existing SO2 oxidation catalysts. The invention achieves nearly double the SO2 conversion efficiency at 400°C compared to conventional commercial catalysts. This higher conversion rate significantly improves the overall efficiency of the SO2 oxidation process, reducing the need for additional catalytic beds or intermediate gas cooling. Its ability to achieve high conversion rates at lower temperatures, combined with its cost-effective and environmentally friendly manufacturing process, makes it a superior solution for industries involved in sulfuric acid production and emissions control.

[0021] OBJECT OF THE INVENTION

[0022] The principal object of the present invention is to provide a cost-effective, highly efficient Vanadia-based catalyst for the oxidation of sulfur dioxide (SO2) to sulphur trioxide (SO3), capable of operating at lower temperatures (around 400°C) while offering significantly improved SO2 conversion rates compared to existing commercial catalysts.

[0023] Specific objectives include:

[0024] 1. To Achieve Higher SO2 Conversion at Lower Temperatures: The invention aims to double the SO2 conversion efficiency at 400°C, thereby improving overall process efficiency and reducing energy consumption in industrial processes such as sulfuric acid production and flue gas desulfurization.

[0025] 2. To Enhance Mechanical Stability of the Catalyst: The invention seeks to provide a catalyst with improved mechanical strength, reducing issues like crushing and pressure drop that are commonly encountered with conventional catalysts.

[0026] 3. To Eliminate the Use of Corrosive Sulfuric Acid in Catalyst Manufacturing: A further object is to develop a manufacturing process that eliminates the need for sulfuric acid (H2SO4), thereby preventing corrosion of equipment, lowering maintenance costs, and improving the sustainability of the production process.

[0027] 4. To Provide an Environmentally Friendly and Cost-Effective Catalyst Solution: The invention is designed to avoid the use of expensive noble metal promoters (such as rhodium and ruthenium) while maintaining high catalytic performance, thus offering a cost-effective and environmentally sustainable solution for industrial SO2 oxidation applications.

[0028] By fulfilling these objectives, the present invention offers significant improvements over existing catalysts, enhancing both the economic and environmental aspects of industrial processes that require efficient SO2 oxidation.

[0029] SUMMARY OF THE INVENTION

[0030] In response to the existing challenges in current technologies, the present invention provides a novel vanadium-based catalyst and a method for its preparation. The invention focuses on improving the uniform distribution of the active catalytic components and enhancing the stability of the carrier material. These improvements result in a catalyst that exhibits higher catalytic activity and better thermal stability compared to conventional catalysts. The catalyst is particularly suited for the oxidation of sulfur dioxide (SO2) into sulfur trioxide (SO3) in the production of sulfuric acid (H2SO4). The catalyst efficiently meets the requirements for total SO2 conversion, thereby holding significant application value in sulfuric acid manufacturing processes.

[0031] In one aspect, the present invention provides a vanadium-based catalyst. The catalyst comprises an active phase that is loaded onto a stable carrier. The active phase primarily consists of vanadium pentoxide (V2O5) combined with alkali metal sulfate / bi sulfate to enhance its catalytic efficiency. The catalyst is supported on a high-stability carrier, typically diatomaceous earth, which improves its mechanical strength and resistance to crushing during operation. This structure ensures the catalyst can operate efficiently at lower temperatures while maintaining high SO2 conversion rates, which is crucial for industrial sulfuric acid production.

[0032] In a preferred embodiment of the present invention, the vanadium-based catalyst is specifically designed to improve the efficiency of the sulfur dioxide (SO2) oxidation process at lower operating temperatures. The catalyst comprises an active phase made primarily of vanadium pentoxide (V2O5) combined with alkali metal sulfate / bi sulfate, which serve as promoters to enhance the catalytic activity. This combination allows the catalyst to achieve higher SO2 conversion rates at approximately 400°C, compared to conventional catalysts that require higher temperatures.

[0033] The carrier material, preferably diatomaceous earth or a similar high-stability material, ensures that the catalyst maintains its mechanical integrity during prolonged operation. The carrier is essential for preventing the catalyst from crushing or degrading over time, which is a common issue in existing commercial catalysts. The improved mechanical stability reduces pressure drop within the catalytic reactor and extends the catalyst’s operational lifespan.

[0034] The embodiment of the invention, a process for producing a catalyst for the oxidation of sulfur dioxide (SO2) to sulfur trioxide (SO3) comprises the following steps:

[0035] In one aspect of the invention, the process begins with the preparation of the support material, which comprises naturally occurring uncalcined diatomaceous earth. The diatomaceous earth used is carefully selected based on its particle size characteristics. The support material includes at least one relatively soft diatomaceous earth that exhibits a percentage reduction of at least 35% in its D50 value when determined using a dry particle size determination method compared to the wet method. This soft diatomaceous earth provides high surface area and enhances the catalytic activity of the final product.

[0036] In another aspect of the invention, a vanadium-containing solution is prepared, which serves as the active phase of the catalyst. The solution or suspension is created by dissolving vanadium pentoxide (V2O5) in a suitable non-corrosive acidic medium, or mild inorganic acids, to form a soluble vanadium salt.

[0037] The vanadium concentration is controlled to ensure uniform impregnation onto the support material. Additionally, alkali metal compounds, are added to the solution to enhance the catalytic performance.

[0038] The process continues with impregnating the support material, wherein the prepared vanadium solution, containing the alkali metal compounds, is mixed with the diatomaceous earth. This ensures uniform distribution of the active catalytic components across the surface of the support. In one aspect of the invention, the impregnation step ensures that the active components are thoroughly distributed, providing consistent catalytic activity throughout the support material.

[0039] In one aspect of the invention, the impregnated material is shaped into the desired form, such as ribbed rings or other structures that maximize surface area and gas flow during operation. The shaping process may involve extrusion or molding to ensure that the catalyst form optimizes gas-solid contact during the SO2 oxidation process.

[0040] The shaped catalyst is dried and calcined, ensuring mechanical strength and activation of the vanadium. In one aspect of the invention, the drying process is performed at temperatures ranging from 100°C to 150°C, followed by calcination at temperatures between 200°C and 550°C. Calcination solidifies the catalyst structure, enhances mechanical stability, and ensures proper activation of the catalytic phase for optimal SO2 conversion performance.

[0041] In another aspect of the invention, the process allows for the incorporation of a relatively hard diatomaceous earth, which has a percentage reduction of less than 35% in its D50 value when determined by the dry method compared to the wet method. This harder diatomaceous earth improves the mechanical durability of the catalyst, making it more resistant to crushing or degradation during extended industrial use.

[0042] In one embodiment, the proportion of relatively soft diatomaceous earth in the support material ranges from 10% to 42% by weight, based on the total mass of the support. This balance between soft and hard diatomaceous earth ensures optimal catalytic efficiency and long-term structural integrity during the SO2 oxidation process.

[0043] In an embodiment, the process described herein comprises the steps of for producing a catalyst for the oxidation of sulfur dioxide (SO2) to sulfur tri oxide (SO3) comprises the following steps:

[0044] 1. Preparation of Vanadium Salt Solution:

[0045] In the first step, vanadium pentoxide (V2O5) is dissolved in an aqueous solution containing an acid with a pKa value in the range of 1 to 4.5. The acid may include suitable acid capable of converting vanadium into a soluble salt form. These acids ensure an environmentally friendly and non-corrosive preparation process.

[0046] The reaction mixture is stirred continuously to ensure complete dissolution of V2O5, forming a blue solution, which indicates the presence of vanadium The resulting vanadium salt solution has a pH of approximately 0.7 to 0.9, ensuring optimal preparation conditions.

[0047] 2. Mixing with Carrier and Promoters:

[0048] In this step, the vanadium salt solution is mixed with a carrier material, preferably diatomaceous earth. The diatomaceous earth serves as a high-surface-area support for the active catalytic components, providing stability and dispersion.

[0049] Along with the vanadium salt solution, alkali metal sulfates or alkali metal bi sulfates are added as promoters to enhance the catalytic activity. The mixture is then thoroughly kneaded or mix milled to ensure even distribution of the active Vanadia components across the surface of the carrier material.

[0050] The resulting mixture achieves uniform dispersion, with the loss on ignition (LOI) at 540°C ranging between 35% and 40%, indicating the proper proportion of active components.

[0051] 3. Shaping of the Catalyst:

[0052] The homogeneous mixture is shaped into the desired form, typically through extrusion. The preferred shape is a ribbed ring, which maximizes surface area and gas-solid contact during the SO2 oxidation process.

[0053] The extruded material is then cut into suitable lengths and prepared for the drying process.

[0054] 4. Drying and Calcination:

[0055] After extrusion, the shaped catalyst is dried to remove any remaining moisture. The drying process is carried out at temperatures between 100°C and 150°C to ensure proper removal of water without disturbing the distribution of the active components. Once dried, the catalyst is subjected to calcination at temperatures ranging from 200°C to 550°C. Calcination serves to solidify the catalyst structure, activate the Vanadia, and improve mechanical stability. This step also enhances the interaction between the Vanadia and the promoter compounds, ensuring optimal catalytic performance.

[0056] The calcination is carried out for several hours to ensure that the Vanadia is fully activated, and the catalyst attains the desired thermal stability.

[0057] 5. Activation of the Catalyst:

[0058] Following calcination, the catalyst is ready for activation. The catalyst is brought to the desired operating temperature of approximately 400°C during the SO2 oxidation process. This activation step ensures that the Vanadia is in its optimal oxidation state for catalysis and that the catalyst is fully functional.

[0059] In another embodiment, the support material can also include at least one relatively hard uncalcined diatomaceous earth, which has a percentage reduction of less than 35% in its D50 value when determined by the same particle size method. This harder diatomaceous earth enhances the mechanical stability of the catalyst, preventing crushing or degradation during prolonged operation, especially in high- temperature industrial environments.

[0060] The catalyst achieves optimal performance when the proportion of relatively soft diatomaceous earth in the total support mass is between 10% and 42% by weight. This ratio ensures the balance between catalytic efficiency, provided by the soft diatomaceous earth, and mechanical durability, ensured by the hard diatomaceous earth.

[0061] Key Advantages of the Process:

[0062] Uniform Distribution of Active Components: The impregnation process ensures even distribution of vanadium and alkali metal compounds, leading to consistent catalytic activity throughout the catalyst structure. Optimized Surface Area: The shaping and calcination steps ensure that the catalyst has a high surface area, promoting efficient gas-solid interactions during the SO2 oxidation reaction.

[0063] Enhanced Mechanical Stability: By incorporating both soft and hard diatomaceous earth, the catalyst maintains mechanical integrity, reducing the likelihood of crushing or material degradation over time.

[0064] Improved Catalytic Efficiency: The catalyst produced by this process achieves double the SO2 conversion efficiency at 400°C, reducing energy consumption and improving overall process efficiency.

[0065] In addition to the key benefits of this preferred embodiment, the invention stands out as a significant advancement compared to previously attempted processes. While earlier efforts have focused on improving SO2 oxidation through the use of alkali metal promoters and noble metals, these solutions have typically required higher operating temperatures, resulting in increased energy consumption. Furthermore, the mechanical instability of prior catalysts, often supported by traditional materials, has led to issues such as crushing, fines generation, and pressure drop, requiring frequent maintenance and limiting catalyst lifespan.

[0066] The present invention addresses these shortcomings by combining high SO2 conversion rates with improved mechanical stability, thanks to the use of diatomaceous earth with specific particle size characteristics. This ensures better resistance to mechanical degradation, preventing the formation of fines that have plagued previous catalysts. Unlike previous processes that relied heavily on costly materials like noble metals, this invention achieves high efficiency at lower temperatures, resulting in significant energy savings and improved process efficiency without the need for expensive components.

[0067] Moreover, the invention employs a corrosion-free manufacturing process by eliminating sulfuric acid (H2SO4) from the preparation steps. Earlier catalyst preparation methods, which relied on H2SO4, often caused corrosion of manufacturing equipment, leading to higher operational costs and environmental concerns. The present invention avoids these pitfalls, making the process not only more efficient but also more sustainable and environmentally friendly.

[0068] In summary, while previous attempts have faced challenges with high energy demands, mechanical degradation, and environmental concerns, this invention provides a robust, energy-efficient, and cost-effective catalyst solution for SO2 oxidation, offering significant advancements over existing technologies.

[0069] The present invention offers solutions to several critical challenges faced in the field of sulfur dioxide (SO2) oxidation and sulfuric acid production:

[0070] Efficient SO2 Conversion at Lower Temperatures:

[0071] The catalyst introduced in this invention is the only type capable of providing 50% SO2 conversion at an operating temperature of 400°C. This is a significant improvement over conventional catalysts, which require higher temperatures to achieve similar conversion rates. The ability to function efficiently at 400°C leads to substantial energy savings and enhances the overall economic feasibility of the process.

[0072] Increased Conversion Efficiency:

[0073] The catalyst achieves 100% more conversion than the benchmark catalyst used in the industry. This dramatic improvement in conversion efficiency means that the new catalyst nearly doubles the output of SO2 to SO3 conversion compared to existing commercial alternatives, further reducing the need for additional reaction stages or scrubbing systems, which simplifies the production process and reduces costs.

[0074] Elimination of H2SO4 in Manufacturing:

[0075] The present invention eliminates the need for sulfuric acid (H2SO4) in the catalyst manufacturing process, which was a key issue in previous technologies. By removing H2SO4 from the production steps, the invention prevents corrosion of manufacturing tools and equipment, leading to lower maintenance costs, longer equipment lifespan, and a more environmentally friendly production process. This not only enhances operational efficiency but also addresses health and safety concerns related to the handling of corrosive substances in industrial settings.

[0076] These and other aspects of the embodiment herein will be better appreciated and understood when considered in conjunction with the following description . It should be understood, however, that the following descriptions, while indicating preferred embodiment and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiment herein without departing from the spirit thereof, and the embodiment herein include all such modifications.

[0077] DETAILED DESCRIPTION

[0078] The embodiments herein and their various features and advantageous details are explained more fully with reference to the non-limiting embodiment provided in the following description. Descriptions of well-known processing techniques are omitted to avoid unnecessarily obscuring the invention. Additionally, the various embodiments described herein are not necessarily mutually exclusive, as some embodiments may be combined with one or more other embodiments to form new embodiments. The term “or” as used herein refers to a non-exclusive or unless otherwise indicated. The examples provided herein are intended to facilitate an understanding of the ways in which the embodiments can be practiced and to further enable those skilled in the art to implement the invention. Accordingly, the examples should not be construed as limiting the scope of the invention.

[0079] Process for Producing the Catalyst

[0080] According to one embodiment, the process for producing a catalyst for the oxidation of sulfur dioxide (SO2) to sulfur trioxide (SO3) comprises the following steps:

[0081] Preparation of the Support Material:

[0082] The process begins by preparing a support material comprising naturally occurring uncalcined diatomaceous earth. The diatomaceous earth used in this process is relatively soft and has a percentage reduction of at least 35% in its D50 value as determined by a particle size distribution analysis using the dry method compared to the wet method. This diatomaceous earth provides a high surface area for the distribution of the active catalytic components.

[0083] Preparation of the Active Solution:

[0084] A solution is prepared containing vanadium pentoxide (V2O5) as the active catalytic component, to form a vanadium salt solution. The concentration of vanadium is controlled to ensure uniform distribution during the impregnation of the support material.

[0085] The solution further comprises alkali metal compounds, Alkali Metal Sulphate (M2SO4) & Bisulfate (HSO4) which act as promoters to enhance the catalyst’s efficiency in the SO2 oxidation process.

[0086] Impregnation of the Support:

[0087] The vanadium-containing solution, along with the alkali metal compounds and sulfate, is thoroughly mixed with the diatomaceous earth support. This ensures that the active components are uniformly distributed across the surface of the diatomaceous earth particles.

[0088] The impregnation process is conducted under controlled conditions to ensure optimal loading of the catalytic components, which allows for high efficiency during SO2 oxidation.

[0089] Shaping the Catalyst:

[0090] The impregnated support material is shaped into a desired form, such as ribbed rings or other structures that maximize surface area and promote efficient gas-solid contact during the catalytic reaction.

[0091] The shaping process may involve extrusion or molding, and the resulting shapes are tailored to the specific needs of the industrial process in which the catalyst will be used.

[0092] Drying the Catalyst:

[0093] After shaping, the catalyst is dried at controlled temperatures ranging from 100°C to 150°C. This step ensures the removal of residual moisture from the impregnation process and prepares the catalyst for calcination.

[0094] Calcination: The dried catalyst is subjected to calcination at temperatures between 200°C and 550°C. Calcination activates the vanadium pentoxide and solidifies the structure of the catalyst, ensuring thermal stability and mechanical strength. This step also enhances the interaction between the vanadium and the alkali metal promoters, which is crucial for optimal catalytic performance.

[0095] Optional Use of Hard Diatomaceous Earth:

[0096] In another embodiment, the process incorporates relatively hard uncalcined diatomaceous earth, which has a percentage reduction of less than 35% in its D50 value as determined by particle size distribution analysis. The inclusion of this harder diatomaceous earth enhances the mechanical stability of the catalyst, making it more durable during long- term operation in high-temperature environments.

[0097] Optimizing the Soft and Hard Diatomaceous Earth Ratio:

[0098] In one embodiment, the proportion of relatively soft diatomaceous earth in the total support material is in the range of 10% to 42% by weight, ensuring a balance between surface area and mechanical strength. This combination allows the catalyst to maintain high SO2 conversion rates while remaining resistant to crushing or degradation during extended use.

[0099] Catalyst Performance

[0100] The catalyst produced by this process is designed to operate efficiently at lower temperatures, typically around 400°C, and offers several key benefits, including: High SO2 Conversion Efficiency: The catalyst achieves nearly double the SO2 conversion rate at 400°C compared to conventional commercial catalysts, making it ideal for industrial processes requiring efficient sulfuric acid production.

[0101] Improved Mechanical Stability: The inclusion of diatomaceous earth ensures resistance to mechanical degradation, reducing the formation of fines and minimizing pressure drop in catalytic reactors.

[0102] Corrosion-Free Manufacturing: The catalyst preparation process does not involve sulfuric acid, preventing corrosion of equipment and making the manufacturing process more environmentally friendly.

[0103] This process allows for the efficient production of a vanadium -based catalyst that addresses the limitations of previous technologies by providing improved catalytic performance at lower temperatures, enhanced mechanical stability, and a more sustainable production process. The catalyst is particularly well-suited for applications in sulfuric acid production and emissions control, where high efficiency and durability are critical.

[0104] The present invention demonstrates a significant advancement in SO2 oxidation efficiency at lower temperatures:

[0105] SO2 Conversion of 50-57% at 400°C: The catalyst developed in this invention reports an impressive conversion rate of 50-57% at an operating temperature of 400°C. This is a remarkable improvement over conventional catalysts, which typically require much higher temperatures to achieve comparable conversion levels. Operating at this lower temperature results in reduced energy consumption and improved operational efficiency.

[0106] Maximum Conversion of 80% at 410°C: The invention further demonstrates maximum SO2 conversions of 80% at 410°C, outperforming benchmark catalysts that require 420°C to achieve similar conversion rates. This 10°C reduction in operating temperature offers significant energy savings and allows for more efficient processing in sulfuric acid production, making the catalyst highly beneficial for industries looking to optimize their processes while maintaining high conversion rates.

[0107] These improvements underline the invention’s capability to enhance both the energy efficiency and productivity of SO2 oxidation processes, providing a cost- effective and environmentally friendly alternative to traditional catalysts.

[0108] EXAMPLES

[0109] The following examples are provided to illustrate the invention and its advantages and are not intended to limit the scope of the invention.

[0110] Example 1: Preparation of Vanadia-Based Catalyst

[0111] A vanadia-based catalyst was prepared using naturally occurring uncalcined diatomaceous earth as a support material. The support comprised a mixture of relatively hard diatomaceous earth and relatively soft diatomaceous earth, wherein the soft diatomaceous earth exhibited a reduction of at least 35% in D50 particle size when measured by dry particle size analysis compared to wet particle size analysis. The ratio of hard to soft diatomaceous earth was maintained at approximately 75:25 by weight.

[0112] Vanadium pentoxide (V2O5) was dissolved in an aqueous solution containing a non- corrosive inorganic acid having a pKa value in the range of 1 to 4.5, resulting in a vanadium salt solution with a pH in the range of 0.7 to 0.9. The solution exhibited a characteristic blue coloration, indicative of vanadium in a reduced oxidation state. An alkali metal promoter selected from alkali metal sulfates and / or bisulfates of potassium, sodium, or rubidium was added to the vanadium salt solution in an amount corresponding to 20-30 wt% relative to the total catalyst composition. The vanadium pentoxide content was maintained in the range of 6-8 wt%.

[0113] The vanadium-promoter solution was impregnated onto the diatomaceous earth support by intensive kneading and mix-mulling to achieve uniform dispersion. The resulting mixture exhibited a loss on ignition (LOI) at 540°C of approximately 35- 40%.

[0114] The impregnated mass was extruded into ribbed ring-shaped catalyst bodies, dried at 100-150°C, and subsequently calcined at temperatures between 200°C and 550°C for several hours to obtain mechanically stable catalyst bodies.

[0115] Example 2: Mechanical Strength Evaluation

[0116] The mechanical strength of the prepared catalyst bodies was evaluated using a ring crush strength test in accordance with ASTM D7084-04. The ribbed ring catalyst bodies exhibited an average crush strength of approximately 8 kg, demonstrating improved resistance to crushing and attrition compared to conventional vanadia catalysts supported on untreated diatomaceous earth.

[0117] Example 3: Catalytic Activity Testing Catalytic activity was evaluated in a laboratory-scale fixed-bed reactor using a catalyst bed volume of 150 cc. The reactor feed gas comprised sulfur dioxide and oxygen under conditions representative of industrial sulfuric acid production.

[0118] SO2 conversion was determined using a titration-based analytical method to measure SO2 and SO3 concentrations at the reactor outlet.

[0119] Catalysts were prepared with varying alkali metal promoter-to-vanadium ratios, and their activities were measured at different operating temperatures. The results are summarized in Table 1. Table 1: Effect of Alkali Metal Promoter-to- Vanadium Ratio on SO2

[0120] Conversion

[0121] Example 4: Performance Analysis

[0122] As shown in Table 1, catalysts containing alkali metal promoter-to-vanadium ratios in the range of approximately 1.1 to 1.7 exhibited significantly enhanced SO2 conversion at 400°C, achieving conversion levels of 57-65%, representing more than a two-fold improvement over catalysts lacking alkali metal promoters.

[0123] The catalyst further demonstrated high conversion efficiency at 410-420°C, reaching conversion values of up to 77-80%, while operating at temperatures lower than those required by conventional commercial vanadia catalysts. This improved low-temperature activity enables reduced energy consumption and enhanced process efficiency in industrial SO2 oxidation applications.

[0124] COMPARATIVE EXAMPLES

[0125] Comparative Example 1: Catalyst Without Alkali Metal Promoter

[0126] For comparative purposes, a vanadia-based catalyst was prepared following the same procedure as described in Example 1, except that no alkali metal sulfate or bisulfate promoter was added to the vanadium salt solution. The catalyst composition, support material, shaping method, drying conditions, calcination temperatures, and catalyst geometry were otherwise maintained substantially identical to those used for the promoted catalysts.

[0127] The comparative catalyst was evaluated under the same laboratory-scale fixed-bed reactor conditions as described in Example 3, using a catalyst bed volume of 150 cc and SO2 conversion analysis by titration.

[0128] The comparative catalyst exhibited SO2 conversion values of approximately 18% at 400°C, significantly lower than the conversion values observed for catalysts prepared in accordance with the embodiments of the present invention containing alkali metal promoter-to-vanadium ratios within the disclosed ranges.

[0129] This comparative example demonstrates that the enhanced SO2 conversion performance observed in the catalysts of the present invention is attributable to the specific combination of vanadia with alkali metal sulfate or bisulfate promoters and the engineered diatomaceous earth support, rather than to vanadia alone or to conventional catalyst preparation methods.

[0130] RESULTS AND ADVANTAGES

[0131] The catalysts prepared in accordance with the embodiments of the present invention demonstrate a combination of performance characteristics that are particularly advantageous for industrial sulfur dioxide oxidation applications.

[0132] The experimental results show that catalysts comprising vanadium pentoxide in combination with alkali metal sulfate and / or bisulfate promoters exhibit significantly enhanced SO2 conversion at reduced operating temperatures. In particular, catalysts having alkali metal promoter-to-vanadium ratios in the range of approximately 1.1 to 1.7 achieved SO2 conversion values of about 57-65% at 400°C, representing a substantial improvement over catalysts lacking alkali metal promoters under identical operating conditions.

[0133] Further, the catalysts demonstrated high conversion efficiencies of up to approximately 77-80% at operating temperatures of about 410-420°C, enabling efficient sulfur dioxide oxidation at temperatures lower than those typically required by conventional vanadia-based catalysts. Operation at reduced temperatures contributes directly to lower energy consumption and improved thermal efficiency in industrial sulfuric acid production processes.

[0134] In addition to enhanced catalytic activity, the catalysts of the present invention exhibited improved mechanical strength and resistance to crushing, as confirmed by ring crush strength testing. The use of a controlled mixture of relatively soft and relatively hard diatomaceous earth provided a balance between high surface area and mechanical durability, thereby reducing fines generation and pressure drop during prolonged reactor operation.

[0135] Moreover, the catalyst preparation process eliminates the use of sulfuric acid and other highly corrosive agents, resulting in a corrosion-free manufacturing process. This reduces equipment degradation, improves workplace safety, and enhances the environmental sustainability of catalyst production.

[0136] Accordingly, the catalysts and methods disclosed herein provide a technically robust, energy-efficient, and industrially scalable solution for sulfur dioxide oxidation, combining improved low-temperature activity, mechanical stability, and environmentally favorable manufacturing characteristics.

Claims

We claim:

1. A vanadia-based catalyst for the oxidation of sulfur dioxide (SO2) to sulfur trioxide (SO3), comprising:I. vanadium pentoxide (V2O5) as an active catalytic component;II. at least one alkali metal promoter selected from alkali metal sulfates, alkali metal bisulfates, or combinations thereof; andIII. a diatomaceous earth support comprising a mixture of relatively soft diatomaceous earth and relatively hard diatomaceous earth, wherein: a) the vanadium pentoxide is present in an amount of 5 to 10 wt%; b) the alkali metal promoter is present in an amount of 20 to 30 wt%; and c) the catalyst exhibits enhanced SO2 conversion at an operating temperature of about 400°C.

2. A process for preparing a vanadia-based catalyst for oxidizing sulfur dioxide (SO2) to sulfur trioxide (SO3), comprising:I. dissolving vanadium pentoxide in an aqueous solution containing a non-corrosive acid having a pKa in the range of 1 to 4.5 to form a vanadium salt solution;II. adding at least one alkali metal sulfate and / or bisulfate promoter to the vanadium salt solution;III. impregnating the solution onto a diatomaceous earth support comprising relatively soft and relatively hard diatomaceous earth;IV. shaping the impregnated material into catalyst bodies;V. drying the shaped bodies at 100°C to 150°C; andVI. calcining the dried bodies at 200°C to 550°C.

3. Use of the catalyst according to claim 1 in a contact process converter or flue gas treatment system for oxidizing sulfur dioxide (SO2) to sulfur trioxide (SO3) at temperatures of about 400°C to 420°C.

4. The catalyst according to claim 1, wherein the alkali metal promoter comprises potassium, sodium, rubidium, cesium, or combinations thereof.

5. The catalyst according to claim 1, wherein the alkali metal promoter comprises potassium sulfate, potassium bisulfate, sodium sulfate, sodium bisulfate, or combinations thereof.

6. The catalyst according to claim 1, wherein the ratio of alkali metal promoter to vanadium is in the range of 0.2 to 1.7.

7. The catalyst according to claim 1, wherein the catalyst exhibits an SO2 conversion of at least 50% at about 400°C.

8. The catalyst according to claim 1, wherein the catalyst exhibits an SO2 conversion of at least 75% at about 410°C to 420°C.

9. The catalyst according to claim 1, wherein the relatively soft diatomaceous earth exhibits a reduction of at least 35% in D50 particle size when measured by dry particle size analysis compared to wet particle size analysis.

10. The catalyst according to claim 1, wherein the relatively hard diatomaceous earth exhibits a reduction of less than 35% in D50 particle size when measured by dry particle size analysis compared to wet particle size analysis.

11. The catalyst according to claim 1, wherein the diatomaceous earth support comprises a weight ratio of hard diatomaceous earth to soft diatomaceous earth of approximately 75:25.

12. The catalyst according to claim 1, wherein the catalyst bodies exhibit a ring crush strength of at least 8 kg, as determined by a ring crush strength test.

13. The catalyst according to claim 1, wherein the catalyst bodies are formed as ribbed rings.

14. The process according to claim 2, wherein the vanadium salt solution has a pH in the range of 0.7 to 0.9.

15. The process according to claim 2, wherein the impregnated material exhibits a loss on ignition (LOI) of 35% to 40% at 540°C.

16. The catalyst according to claim 1, wherein the presence of the alkali metal promoter results in a higher SO2 conversion at about 400°C compared to an otherwise identical catalyst lacking the alkali metal promoter.Dated, 19thday of December, 2025

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